This invention relates to engraving heads of the general type disclosed in Buechler U.S. Pat. No. 4,450,486. Such engraving heads comprise a diamond stylus carried by a holder mounted on an arm projecting from a torsionally oscillated shaft. A sine wave driving signal is applied to a pair of opposed electromagnets to rotate the shaft through a maximum arc of approximately 0.25xc2x0 at a frequency in the neighborhood of about 3,000 to 5,000 Hz.
A guide shoe is mounted on the engraving head in a precisely known position relative to the oscillating stylus. The engraving head is supported for tilting movement by a set of leaf springs secured to a rearwardly projecting bar. A DC motor rotates the bar so as to bring the guide shoe into contact with a printing cylinder to be engraved. When the guide shoe is in contact with the printing cylinder, the stylus oscillates from a position just barely touching the printing cylinder to a retracted position about 100 microns distant from the surface of the cylinder.
Once the guide shoe is in contact against the printing cylinder a video signal is added to the sine wave driving signal for urging the oscillating stylus into contact with the printing cylinder thereby engraving a series of controlled depth cells in the surface thereof. The printing cylinder rotates in synchronism with the oscillating movement of the stylus while a lead screw arrangement produces axial movement of the engraving head so that the engraving head comes into engraving contact with the entire printing surface of the printing cylinder.
In engraving systems of the type taught by Buechler, it is necessary for the machine operator to perform a tedious trial and error setup procedure at one end of the printing cylinder prior to commencement of engraving. This procedure involves adjustment of the gain on amplifiers for the sine wave driving signal and the video signal so as to produce xe2x80x9cblackxe2x80x9d printing cells of a desired depth together with connecting channels of another desired depth and clean non-engraved white cells or areas. Each change of one of the control variables interacts with the others, and therefore the setup becomes an iterative process.
There is also a need in the engraving industry to provide an engraving system and apparatus with imaging and focusing capabilities which further facilitate automatically focusing on a surface of the cylinder and subsequently capturing images and measuring engraved areas on the surface. What is also needed is an engraving system which can quickly measure a dimension of a cut or cell, for example, of precisely controlled dimensions during set-up or real-time operation of the engraver.
There is a further need to provide a system and method for processing data corresponding to captured images, for example, by eliminating undesired image data or filling in discontinuous data corresponding to gaps in the array of data which correspond to gaps in a captured image.
What is also needed is an engraver comprising an apparatus or method for scaling or calibrating the intensity of light used in the focusing process to enhance automatically focusing, measuring and engraving cuts of precisely controlled dimensions.
It has been found that electronic images of engraved areas on copper printing cylinders can be captured with a charge-coupled device (CCD) and digitally processed to obtain measurements of the engraved areas using various prior art techniques. Typically, images of engraved areas show up as isolated dark regions where the incident light has been defracted out of the optical system due to multiple reflections within the interior of the engraved area. However, the quality of the captured images can be degraded by various artifacts or image noise which can occur individually or in combination. Some of the sources of these artifacts are wear of the diamond stylus used to engrave the engraved areas, ambient light, and uneven or inconsistent illumination over the imaged region.
The diamond engraving stylus used to engrave areas is susceptible to wear and xe2x80x9cchipagexe2x80x9d during engraving which, in turn, alters the interior shape of the engraved areas. This can result in significant levels of optical energy being reflected back into the optical system rather than defracted out of the optical system. Such energy shows up as bright spots on top of the otherwise dark engraved cells, hereinafter referred to as xe2x80x9cglarexe2x80x9d and can result in inaccurate measurements of the engraved area. Ambient light (from room lighting reflecting off the copper surface and the engraved areas) can also contribute to this glare.
Inconsistent or uneven illumination of the engraved areas creates further image noise in the electronic images which can result in inconsistent measurements of the engraved areas. If the luminous intensity upon the copper surface is too bright, xe2x80x9cbloomingxe2x80x9d can occur in the CCD, thereby resulting in electronic measurements or dimensions which are smaller than the actual measurements or dimensions of the engraved area. When the luminous intensity is too dark, the edges of the engraved areas blend into the background surface of the copper, which causes electronic measurements which are larger than the actual engraved measurements.
FIG. 20 illustrates one prior art technique for attempting to reduce some or all of the aforementioned problems encountered in the past. In particular, this technique employs a Xenon flash bulb 800 which, when energized, flashes light through a fiber optic bundle 804 through a linear polarizer 810. After being polarized, the light travels though a collimating lens 812 where it contacts a 50-50 beamsplitter 814 and passes through objective lens 816 onto surface 802a of cylinder 802. Thereafter, it is reflected back through objective lens 816, through beamsplitter 814, and captured by CCD array 808a of camera 808. While the placement of a single polarizer in line with the light source before it is reflected onto surface 802a of cylinder 802 has facilitated overcoming some of the aforementioned problems, what is needed is an engraver, system and method having an improved image system for imaging of engraved areas and facilitating reducing problems of the past, including problems resulting from diamond wear, inconsistent illumination, xe2x80x9cbloomingxe2x80x9d, glare and the like.
It is therefore seen that a need has existed for an engraving system having image means which may be quickly and easily set up to engrave cells of precisely controlled dimensions in the surface of a gravure printing cylinder.
In one aspect, this invention comprises a method for adjusting an engraver to engrave a cylinder with an actual cut according to predetermined setup parameters, said method comprising the steps of: (a) determining an error value corresponding to the difference between said predetermined setup parameters and an actual measurement of a portion of an engraved area on said cylinder; and (b) using said error value to adjust said engraver to engrave said actual cut in accordance with said predetermined setup parameters.
In another aspect, this invention comprises a method for measuring a portion of an engraved area on a cylinder in an engraver, said method comprising the step of generating a plurality of actual dimension values corresponding to said portion.
In still another aspect, this invention comprises a system for measuring a portion of an engraved area on a cylinder in an engraver, said system comprising a measuring device for generating a plurality of actual dimension values corresponding to said portion.
In yet another aspect, this invention comprises an error correction system for use in an engraver suitable for engraving a cylinder with an actual cut in accordance with predetermined setup parameters, said error correction system comprising determining means for determining an error value corresponding to the difference between the predetermined setup parameters and a measurement of the actual dimensions of a portion of an engraved area on said cylinder; and a system coupled to said determining means for receiving said error value and also for adjusting said engraver to engrave said actual cut in accordance with said predetermined setup parameters.
In still another aspect, this invention comprises a method for measuring a portion of a cylinder in an engraver, the method consists of the steps of focusing on a focus area of cylinder with an imager, imaging the portion with the imager, generating an array of data corresponding to the portion, and determining at least one actual dimension value using the array of data.
In another aspect, this invention comprises a system for imaging an area of a cylinder in an engraver, the system comprising an imager for capturing an image of the engraved area and a video processor coupled to the imager for generating a plurality of dimension values corresponding to the image, the imager comprising an illuminator capable of illuminating the area to a plurality of light intensity levels.
In another aspect, this invention comprises an engraver for engraving a plurality of cells on a surface of a cylinder engraver consisting of a support for rotatably supporting the cylinder, an engraving head for engraving the cylinder, the engraving head being mounted in operable relationship with the cylinder when the cylinder is rotatably mounted on the cylinder, and an image system associated with the engraving head for capturing an image of an area on the surface.
In a still further embodiment, a method for imaging an area of a surface of a cylinder comprises the steps of supporting the cylinder on an engraver in operative relationship with an engraving head, imaging the area of the cylinder with an imager associated with the engraving head to provide image data, and focusing the imager on a surface of the cylinder using the image data.
The present invention also provides an engraving apparatus and method wherein a plurality of parameter signals are supplied to a setup circuit or computer for computing engraving parameters to control the engraving response of the engraving stylus to an input video signal. An input AC signal and an input video signal are multiplied by multiplication factors which are generated by the computer. The computer also generates a white offset signal which is combined with the above mentioned multiplication factors to produce a driving signal for the engraving stylus. The stylus then engraves cells of the desired geometry.
The computer is provided with input signals which indicate a desired black cell width, a desired channel width, a desired highlight cell width and the video voltage level at which a highlight cell of the desired width is to be engraved. The values of these parameters are used for solving a set of equations which produce the appropriate values for the two multiplication factors and the white offset.
A video camera is operated to produce a frame of video information including an image of an engraved area, such as a cell, which has been engraved by a video signal of a predetermined level. A video processing circuit measures the width of the cell which has been so imaged and reports it to the computer. The computer then adjusts the multiplication factors and the white offset through use of an error term which is equal to the difference between the expected cell width and the measured cell width.
Another object is to provide a system and method for improving the imaging of engraved areas by facilitating reducing poor imaging resulting from glare, inconsistent illumination, xe2x80x9cbloomingxe2x80x9d and the like.
Another object of the invention is to provide an improved optical system comprising at least one polarizer suitable for polarizing light reflected from a surface of a cylinder.
Still another object of the invention is to provide a simplified illuminator in the form of a light emitting diode (LED) for illuminating an area.
In one aspect, this invention comprises an engraver for engraving at least one cell on a surface of a cylinder, the engraver comprising a support for rotatably supporting the cylinder, an engraving head for engraving the cylinder, the engraving head being mounted in operable relationship with the cylinder when the cylinder is rotatably mounted on the engraver and an imaging system associated with the engraving head for capturing an image of an area on the surface, the imaging system comprising at least one polarizer for polarizing light reflected from the cylinder to facilitate reducing undesired image noise associated with the image.
In another aspect, this invention comprises a system for imaging an area of a cylinder engraved by an engraver, the system comprising an imager for capturing an image of the engraved area, the imager comprising an illuminator capable of illuminating the area to a plurality of light intensity levels and at least one polarizer for polarizing light generated by the illuminator.
In still another aspect, this invention comprise a method for imaging an area of a surface of a cylinder engraved by an engraver comprising the steps of supporting the cylinder on an engraver in operative relationship with an engraving head, illuminating the area with light generated by an illuminator, polarizing the light generated by the illuminator, imaging the area of the cylinder with an imager associated with the engraving head to provide image data and focusing the imager on a surface of the cylinder.
In yet another aspect, an engraver for engraving at least one engraved area on a surface of a cylinder, the engraver comprising a support for rotatably supporting the cylinder, an engraving head for engraving the cylinder, the engraving head being mounted in operable relationship with the cylinder when the cylinder is rotatably mounted on the engraver and an imaging system associated with the engraving head for capturing an image of an area on the surface, the imaging system comprising at least one LED for illuminating the area on the surface.
Other objects and advantages of the invention will be apparent from the following description, the accompanying drawings, and appended claims.